This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Non-invasive, regional assessment of lung function has the potential to markedly enhance the monitoring of progression of pulmonary diseases, as well as quantitative assessment of response to therapeutic intervention. Quantitative hyperpolarized (HP) 3He MRI techniques have emerged over the past decade to address crucial aspects of both lung structure and function. Alveolar partial pressure of oxygen is one of the important pulmonary markers with high sensitivity to alterations of regional lung physiology. The basic principle for measurements of partial pressure of oxygen is based on the characteristic relaxation time constant of HP 3He in presence of oxygen. Different methods have been developed to distinguish oxygen-induced decay from RF-induced decay. A single acquisition scheme was developed earlier as part of this project, spaced unequally in time, and optimally configured to extract oxygen tension, uptake rate, or some combination thereof. To constrain the four free parameters (initial intensity, oxygen tension, uptake rate, flip-angle) independently for each voxel requires, at minimum, four images;practical implementations therefore require a compromise between imaging resolution and tolerable breath-hold. In order to improve the achievable spatial resolution in 3 dimensions we eliminate the oxygen uptake fit parameter and use an off-line calibration procedure to constrain the flip-angle individually for each voxel. This requires only two images and results in a breath-hold which is tolerable for all but the most severely diseased subjects.